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<span id="Generating-your-own-code-1"></span><h3 class="section">10.4 Generating your own code</h3>
<span id="index-code-generator-1"></span>

<p>The directory <code>genfft</code> contains the programs that were used to
generate FFTW&rsquo;s &ldquo;codelets,&rdquo; which are hard-coded transforms of small
sizes.
<span id="index-codelet-2"></span>
We do not expect casual users to employ the generator, which is a rather
sophisticated program that generates directed acyclic graphs of FFT
algorithms and performs algebraic simplifications on them.  It was
written in Objective Caml, a dialect of ML, which is available at
<a href="http://caml.inria.fr/ocaml/index.en.html">http://caml.inria.fr/ocaml/index.en.html</a>.
<span id="index-Caml"></span>
</p>

<p>If you have Objective Caml installed (along with recent versions of
GNU <code>autoconf</code>, <code>automake</code>, and <code>libtool</code>), then you
can change the set of codelets that are generated or play with the
generation options.  The set of generated codelets is specified by the
<code>{dft,rdft}/{codelets,simd}/*/Makefile.am</code> files.  For example, you can add
efficient REDFT codelets of small sizes by modifying
<code>rdft/codelets/r2r/Makefile.am</code>.
<span id="index-REDFT-2"></span>
After you modify any <code>Makefile.am</code> files, you can type <code>sh
bootstrap.sh</code> in the top-level directory followed by <code>make</code> to
re-generate the files.
</p>
<p>We do not provide more details about the code-generation process, since
we do not expect that most users will need to generate their own code.
However, feel free to contact us at <a href="mailto:fftw@fftw.org">fftw@fftw.org</a> if
you are interested in the subject.
</p>
<span id="index-monadic-programming"></span>
<p>You might find it interesting to learn Caml and/or some modern
programming techniques that we used in the generator (including monadic
programming), especially if you heard the rumor that Java and
object-oriented programming are the latest advancement in the field.
The internal operation of the codelet generator is described in the
paper, &ldquo;A Fast Fourier Transform Compiler,&rdquo; by M. Frigo, which is
available from the <a href="http://www.fftw.org">FFTW home page</a> and also
appeared in the <cite>Proceedings of the 1999 ACM SIGPLAN Conference on
Programming Language Design and Implementation (PLDI)</cite>.
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